The structural investigation on small methane clusters described by two different potentials

Abstract

Structures of molecular clusters have not been well elucidated. In the present study, a fundamental cluster (CH 4 ) n (n ≤ 40) was theoretically investigated with two potentials; one is a well-known potential called OPLS and the other is a Morse potential obtained from ab initio calculations of the methane dimer. The global minima of methane clusters were searched with the heuristic method combined with geometrical perturbations. The local structure analysis of the global-minimum geometries of the clusters shows that they contain spherical geometries where twelve to sixteen molecules surround a molecule. The structural growth sequences of the OPLS and Morse-potential-based clusters were examined with rotational constants of them and core structures formed by interior molecules. The global-minimum geometries of most of the OPLS clusters with n ≤ 30 are similar to those of the corresponding Morse-potential-based clusters.

Synthesis of DNL‐6 with a High Concentration of Si (4 Al) Environments and its Application in CO2 Separation

“…A possible reason is that CH 4 molecules form small clusters because of intermolecular interactions caused by the Lennard-Jones potential, which was demonstrated by theoretical calculations. [41] Thus, CH 4 cannot freely pass through the pores of the M-DNL-6 adsorbent, and the true adsorption equilibrium is not reached. Palomino et al observed similar phenomena when they studied CH 4 adsorption on the RHO zeolite.…”

Theoretical Study of Methane Storage in Cu24(m-BDC)24

“…An alternative starting geometry also considered was the lowest-energy structure from a heuristic method to locate the global minimum on the OPLS potential energy surface. 41,42 In all cases except for the (CH 4 ) 4 cluster, the lower-symmetry starting structure produced stronger binding energies ( 37 The Cu−Cu distances in the Cu 2 O 8 units are slight too short, probably due to the absence of coordinated DMF and H 2 O molecules in the calculated structure. However, the Cu−O and cross-ring Cu−Cu distances are predicted very well.…”

“…As a preliminary to the study of CH 4 binding in the Cu 24 ( m -BDC) 24 cage, the binding energies of CH 4 clusters were calculated. − Symmetrical complexes were considered with D 3 d and S 4 symmetries (Figure ). An alternative starting geometry also considered was the lowest-energy structure from a heuristic method to locate the global minimum on the OPLS potential energy surface. , In all cases except for the (CH 4 ) 4 cluster, the lower-symmetry starting structure produced stronger binding energies (Table ). The binding energies of the CH 4 clusters are in good agreement with previous work employing force field and DFT calculations (Table ).…”

“… a Ref . b Ref . c Geometry optimization started from the lowest-energy PBE0-DCP/6-31+G­(d,p) optimized methasne cluster structure (ref ). d Binding energy per CH 4 is 0.60 kcal/mol at the CCSD­(T)/CBS level (ref ). …”

Structure, Reactivity, and Fragmentation of Small Multi-Charged Methane Clusters

“…For the neutral (CH 4 ) 4 tetramer, rhombic and pyramidal isomers (Figure 2) are computed to be stable in agreement with those of Takeuchi. 35 For (CH 4 ) 4 + , a proton is shared between two methane units. This charge transfer complex may dissociate later to produce CH 3 + CH 5 (CH 4 ) 2 + .…”